The present invention relates to a system for the treatment of disorders of the vasculature, particularly aneurysms. An aneurysm is a medical condition indicated generally by an expansion and weakening of the wall of an artery of a patient. Aneurysms can develop at various sites within a patient's body. Thoracic aortic aneurysms (TAAs) or abdominal aortic aneurysms (AAAs) are manifested by an expansion and weakening of the aorta which is a serious and life threatening condition for which intervention is generally indicated. Existing methods of treating aneurysms include invasive surgical procedures with graft replacement of the affected vessel or body lumen or reinforcement of the vessel with a graft.
Surgical procedures to treat aneurysms can have relatively high morbidity and mortality rates due to the risk factors inherent to surgical repair of this disease, as well as long hospital stays and painful recoveries. Due to the inherent risks and complexities of surgical repair of aortic aneurysms, endovascular repair has become a widely used alternative therapy, most notably in treating AAAs. Early work in this field is exemplified by Lawrence, Jr. et al. in “Percutaneous Endovascular Graft: Experimental Evaluation”, Radiology (May 1987) and by Mirich et al. in “Percutaneously Placed Endovascular Grafts for Aortic Aneurysms: Feasibility Study,” Radiology (March 1989). Commercially available endoprostheses for the endovascular treatment of AAAs include the Endurant® stent-graft system manufactured by Medtronic, Inc. of Minneapolis, Minn., the Zenith® stent-graft system sold by Cook, Inc. of Bloomington, Ind., the PowerLink® stent-graft system manufactured by Endologix, Inc. of Irvine, Calif., and the Excluder® stent-graft system manufactured by W.L. Gore & Associates, Inc. of Newark, Del. A commercially available stent-graft for the treatment of TAAs is the TAG™ system manufactured by W.L. Gore & Associates, Inc.
In order for aortic endografts to be applied to more patients, their ability to address aneurysms that involve major branch vessels (e.g., left subclavian for thoracic, renals for abdominal, SMA and celiac for thoraco-abdominal) is helpful. One common approach has been through the use of graft fenestrations combined with separate stent-grafts or stents deployed within the branch vessel and through the graft fenestrations (often flared via ballooning to secure the junction). Another technique has been the use of branched endografts in which appendages (branches) are integrated into the main graft.
Both of these approaches have, however, required custom made endografts, with the fenestrations located at the positions of the patient's branch vessels, or for branched grafts, the branches are similarly custom-positioned during device manufacture. These techniques also increase procedural time and complexity significantly and run the risk of inadvertent branch vessel coverage, which can lead to emergent surgical conversion.
More recent approaches are aimed at allowing off the shelf devices to be used. These devices have pre-made fenestrations in a portion of the graft that is unsupported and has redundant material that allows the fenestrations to be moved a limited amount relative to the main graft to allow for the patient to patient variability in branch vessel locations.
Other concepts have included burning or boring fenestrations via access through the branch vessel into the endograft post deployment, but no such approach has been adopted with a commercial as of yet.
Yet another technique is the use of chimney (and/or “snorkel” at the distal end) grafts in combination with a conventional endograft. These separate chimney stent-grafts preserve the branch vessel's patency and typically are positioned between the aortic wall and main endograft, with their other end projecting beyond the edge of the main graft. The chimney is positioned in the body before the main graft is deployed, so if difficulty is encountered in chimney deployment, the chimney may be repositioned and/or redeployed before deployment of the main endograft. In contrast, with fenestrated devices the main device is deployed before access to the branch vessels is completed, which contributes to procedural and device complexity.
Several clinical studies in this context have been described in the literature (see, e.g., Giovanni Torsello et al., “Breaking Barriers: Expanding the EVAR Population”, Supplement to Endovascular Today, November 2010, pages 16-18 (using Medtronic Endurant® peripheral stent-grafts)). The challenge in many of these cases is that the round cross section peripheral stent-graft typically used for the branch vessel can pose a sealing challenge for the main stent-graft. Two “gutters”, or areas of potential blood leakage, are typically left behind, since the main graft cannot conform fully to the round cross section chimney (which may ovalize somewhat) yet must be stiff enough to resist collapse and prevent branch vessel occlusion. Such blood leakage, if it occurs, can result in clinical problems and even failure of the endograft in performing its task of excluding the aneurysm into which it is deployed.